Radioactive tracers



United States Patent 3,014,054 RADIOACTIVE TRACERS Bernard A. Fries, Orinda, Calif., assignor to California This invention relates to liquid radioactive tracers and methods for their preparation, and particularly refers to a stable oil soluble tracer consisting essentially of a sulfonate prepared from isotopes of gold that may be used in extreme dilutions in liquid hydrocarbons or other oil solvents.

Heretofore it has been proposed to prepare and to untilize oil soluble sulfonates of radioactive isotopes having a moderate specific activity and long half-life, such as Cs and Cs as exemplified in my United States Patent No. 2,835,699, issued May 20, 1958. These are useful in measuring and tracing fluid flow in pipe lines, oil refining processes and the like, as exemplified in United States Patents 2,706,254 (Hull and Mithoff) and 2,826,699 and 2,826,700 (Hull).

Under certain conditions it is essential to provide an oil soluble radioactive tracer that not only has a short half-life and a high specific activity but also will be stable for reasonably long periods of time under conditions of extreme dilution, e.g. one part of tracer in several million parts of oil. The need for a short half-life radiotracer may arise where repeated additions of tracer are necessary. The use of a long-lived tracer would result in higher and higher concentrations of the radioisotope in the system. However, because nearly all the radioisotopes of gold have half-lives of a few days or less, their decay is rapid and there is no significant build-up of radioactivity with time. Even in single additions of gold tracer, rapid decay assures rapid removal of the radioactivity in the system.

I have found that the procedure described in my Patent 2,835,699, when applied to the preparation of an oil soluble sulfonate of a gold isotope, did not result in a stable product, i.e. under the conditions just outlined the results of its use were erratic and unpredictable. Large proportions of the radioactivity (ten percent or more) frequently separated from the sulfonate preparation after only slight dilution with liquid hydrocarbons.

It is an object of this invention to provide an improved procedure for preparing an oil soluble and water insoluble radioactive liquid tracer composition that will be safe and convenient to use, and will remain stable in extreme dilutions in liquid hydrocarbons.

Another object is to provide a new and useful product, viz. a stable, oil soluble sulfonate of an isotope of gold.

Another object is to provide a new and useful product, viz. a stable, oil soluble sulfonate of Au Another object is to provide a new and useful product, viz. a stable, oil soluble sulfonate of Au These and other objects and advantages will be further apparent from the following specification, which describes the improved product and exemplary procedures for preparing it.

The radioactive isotopes of gold, Au and Au are available for qualified users from Oak Ridge National Laboratory of the United States Atomic Energy Commission as a dilute solution in acid (mixed HCl and HNO having a very high specific radioactivity and thus requiring shielded handling, as is well known in this art. The final product also requires suitable monitoring procedures and equipment for safe storage and utilization.

Example I In this example, a 1.0 ml. (milliliter) aliquot of gold- 198 chloride solution containing 2 me. millicuries) of Au activity and 0.5 mg. (milligram) of total elemental gold Was evaporated to dryness to remove the excess acid. The dry residue was taken up in 2 ml. of tap water, and 10 ml. of calcium petroleum mahogany sulfonate was added. The mixture was heated gently with stirring until the water was evaporated. The final product was dissolved in one pint of light petroleum solvent and resulted in a clear, bright solution which remained stable indefinitely on storage. the original starting activity was recovered in the final product solution. The remaining three percent of -the activity adhered to the reaction vessel in an insoluble form. This oil soluble product is considered to be a sulfonate, or, more specifically, a calcium sulfonate of Au and is so designated herein. The specific activity of the calcium-gold sulfonate preparation and the final diluted tracer may be chosen to suit the particular use to which the product may be put.

Example II In this example, a 1.0 ml. aliquot of gold-198 chloride solution containing 2 me. of Au activity and 0.5 mg. of total elemental gold was evaporated to dryness to remove the excess acid. The dry residue was taken up in 2 ml. of a dilute NaCN solution (about one percent NaCN in tap water) after which 10 ml. of calcium petroleum mahogany sulfonate was added. The mixture was heated gently with stirring until the water was evaporated. The final product was dissolved in one pint of light petroleum solvent and resulted in a clear, bright solution, which is considered to be a NaCN-stabilized sulfonate, or, more specifically, a NaCN-stabilized calcium sulfonate of Au and is so designated herein. About 99.8 percent of the original starting activity was recovered in the final product solution, while only 0.2 percent adhered to the reaction vessel. In the presence of NaCN, gold is strongly complexed to form aurocyanide. In this complex the reduction of gold to the insoluble metallic form by organic reducing materials in the presence of a slight excess of alkali is effectively prevented. This may account for the improved yield and the somewhat more stable product.

NaCl is described as a suitable stabilizer, and it is apparent that KCN could also be employed. Likewise there are various calcium sulfonates that are available commerically, e.g., Oronite Lubricating Oil Additive (OLOA) Nos. 246A, 246B, and 1054, sold by Oronite Chemical Company, San Francisco, California.

The radioactive and other properties of the gold isotope products of this invention are very desirable for certain tracer applications, for example, tracing petroleum products in refinery equipment. These isotopes emit several gamma rays that are of suitable magnitude to penetrate the steel wall of a pipe line or of a tank or reaction vessel and may be detected outside of the pipe or tank by suitable gamma-ray detectors. The most readily available radioisotopes of gold are Au and Au The isotope Au having a half-life of 2.70 days, emits principally a gamma ray of 0.412 mev. energy. The isotope Au having a half-life of 3.15 days, emits several gamma rays, the most energetic of which has an energy of 0.21 mev.

The isotope Au is the preferred one of the above two radioisotopes. Smaller quantities are required because of its more energetic gamma ray, and it is one of the least expensive of all radioisotopes, currently sold by Oak Ridge National Laboratories of the United States Atomic Energy Commission for $0.06 per mc. compared to $3.00 per me. for Au Although only two examples of this procedure and products therefrom are described above, it is apparent Ninety-seven percent of 3 that numerous substitutions could be made, e.g., KCN for NaCN, and all such changes that come within the scope of the appended claims are intended to be embraced thereby.

I claim:

1. A radioactive tracer consisting essentially of a stable oil soluble sulfonate of an isotope of gold selected from the group consisting of Au and Au 2. A radioactive tracer consisting essentially of a stable oil soluble sulfonate of Au 3. A radioactive tracer consisting essentially of a stable oil soluble sulfonate of Au 4. A radioactive tracer consisting essentially of a sulfonate obtained by reacting an oil soluble calcium sulfonate and an inorganic gold salt, wherein the gold is selected from the group consisting of radioactive isotopes Au and Au 5. A radioactive tracer according to claim 4 in which the tracer is stabilized with NaCN.

6. A method of preparing a radioactive tracer com- 20 prising the steps of reacting an oil soluble calcium sulfonate and a radioactive gold isotope selected from the References Cited in the file of this patent UNITED STATES PATENTS 2,058,774 Colligan Oct. 27, 1936 2,206,634 Fermi et al July 2, 1940 2,835,699 Fries May 20, 1958 FOREIGN PATENTS 795,028 Great Britain May 14, 1958 UNITED STATES PATENT OFFICE Patent No. 3,014,054

December 19., 1961 Bernard A. Fries It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column l line 16, for untilize" read we utilize column 2, line 44,, for "NaCl" read we NaCN s (SEAL) Attcst:

ESTON G. JOHNSON Attesting Officer DAVID L. LADD Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No 3 Ol4 O54 December 19 1961 Bernard Aa Fries It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below,

Column l line 16 for "untilize" read me utilize eo-lumn 2 line 44 for NaC1" read me NaCN e Signed and sealed this 24th day of April 1962o (SEAL) Attest:

ESTQN Go JOHNSON DAVID Lo LADD Attesting Officer Commissioner of Patents 

1. A RADIOACTIVE TRACER CONSISTING ESSENTIALLY OF A STABLE OIL SOLUBLE SULFONATE OF AN ISOTOPE OF GOLD SELECTED FROM THE GROUP CONSISTING OF AU198 AND AU199. 